The present invention relates to a method for stabilizing phenylacetaldehyde against polymerization and autocondensation.
Phenylacetaldehyde occurs in essential oils and is a volatile constituent of foods. Its odor resembles hyacinth. Phenylacetaldehyde can be prepared by a rearrangement of styrene oxide and is used in fragrance compositions and flavorings; K. Bauer, A. Garbe, Common Fragrance and Flavor Materials, p. 68, VCH, Weinheim, 1985; S. Steffen Arctander, Perfume and Flavor Chemicals, No. 2470, Montclair, N.J., USA 1969.
Phenylacetaldehyde, owing to its high reactivity, has a tendency towards polymerization and autocondensation. In polymerization, predominantly 2,4,6-tribenzyl-1,3,5-trioxane forms. Trimerization is catalyzed by the presence of chemical substances such as chlorine or bromine, phosphorus pentoxide, sulfuric acid, hydrogen sulphide, hydrogen chloride, hydrogen fluoride, boron trifluoride, aluminum chloride, iron chloride or zinc chloride. In the presence of acidic compounds, the polymerization of phenylacetaldehyde begins spontaneously. Furthermore, low temperatures from about 0xc2x0 C., or UV light, promote polymerization.
A further problem is the tendency of phenylacetaldehyde to be subjected to aldol condensation in the presence of alkaline substances.
It is known that the polymerization and autocondensation reactions of aldehydes can be prevented by the addition of certain substances. In the processing and use of phenylacetaldehyde as a fragrance and flavoring, the added chemical substances must not interfere organoleptically and must be permissible under food legislation.
DE-A 29 05 267 and DE-A 29 17 789 disclose that aliphatic aldehydes can be stabilized against polymerization and autocondensation by adding triethanolamine or dimethylethanolamine. However, a disadvantage of these stabilizers is that they are undesirable in foods and can only be removed again from the aldehydes by complex distillation.
JP 45 012282 B4 and DE A 19757531 describe the stabilization of aliphatic aldehydes by alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates or alkaline earth metal carboxylates. A disadvantage of this method is that the substances added do not dissolve and disperse completely. A uniform distribution of the alkaline substance in the entire volume of aldehyde is difficult to achieve.
SU A 1705273 describes the stabilization of phenylacetaldehyde by combining three classes of substances; i.e.
1. a free-radical scavenger such as alpha-tocopherol or butylated hydroxyanisole
2. a diphenylamine derivative such as dimethylbis(p-phenylaminophenoxy)silane and
3. a hydroxy acid such as tartaric acid, ascorbic acid or citric acid.
A disadvantage of this method is the extensive usage of substances. In addition, the diphenylamine derivatives described are not permitted in foods.
Therefore, it is an object of the present invention to provide a method for stabilizing phenylacetaldehyde by adding one or more additives, which method does not have the abovementioned disadvantages.
A method has been found for stabilizing phenylacetaldehyde by adding one or more additives wherein the additives contain one or more polybasic carboxylic acids.
According to the present invention, the polybasic carboxylic acids are used in amounts of 10 to 1,000 ppm. Preference is given to 100 to 300 ppm.
Polybasic carboxylic acids, which come into consideration are in particular, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, citric acid, maleic acid or fumaric acid.
The carboxylic acids, which come into consideration, are harmless in the food sector. Therefore, it is no longer necessary to remove unwanted substances with considerable effort. It is also advantageous that the carboxylic acids described are completely soluble and dispersible. This ensures even distribution in the volume of aldehyde. The consequence is optimum stabilization of the phenylacetaldehydes present. It is surprising that addition of polybasic carboxylic acids alone, that is to say without using other additives, achieves the advantages described. The inventive method is, thus, also very simple and inexpensive.
The present invention relates to an additive-containing phenylacetaldehyde. This additive is characterized in that it contains one or more polybasic carboxylic acids.
In addition, the present invention relates to the use of the stabilized phenylacetaldehyde for preparing fragrance compositions and flavorings.